1. Field of the Invention
The invention relates to a semiconductor circuit apparatus, more particularly, a semiconductor circuit apparatus having a power save mode and an active mode.
2. Description of Related Art
Semiconductor technological advances and more multifaceted and sophisticated products have given rise to demand for faster, more sophisticated, larger scale and less power consumption semiconductor circuits. In order to meet such demand, semiconductor chips with system on chip structure, in which multiple circuit blocks of different functions are formed, are widely used. Further, semiconductor circuit chips which have multiple operation modes are proposed to reduce the power consumption. Such electrical products have a standby mode, which is a power save mode, in which a part of the circuit is deactivated so that the standby power consumption is reduced.
One typical example of electric device with the standby mode is a handheld mobile device, such as a cellular phone and PDA (Personal Digital Assistance). Since the mobile devices use a battery as a power supply and there is a demand for long continuous use, the reduction of power consumption of semiconductor circuit chips is highly demanded. Furthermore, as more sophisticated cellular phones are introduced, more sophisticated and higher operation speed semiconductor circuit chips are significantly required.
Though a cellular phone needs to operate constantly in preparation for incoming calls, not all the circuit needs to operate constantly. Power consumption reduction is accomplished by activating only the necessary circuits during the standby period. An increase of the drive voltage results in higher speed circuit, but an increase in the drive voltage can lead to increased power consumption. Therefore, a technique is proposed which reduces the drive voltage and the thickness of gate insulating film of a device to accomplish reduced power consumption, as well as achieving high speed operation with increased on-current.
FIG. 10 is a schematic block diagram of a related semiconductor circuit apparatus having multiple circuit blocks and a standby mode as an operation mode. A semiconductor circuit apparatus comprises the first circuit block 1001, the second circuit block 1002 and I/O circuit part 1003. The first and second circuit blocks 1001, 1002 have a processor, a memory, an analog circuit portion part and a digital circuit part, respectively. Each of circuit blocks 1001-1003 has an interface control circuit.
FIG. 11 shows the power supply voltage levels in an active mode and a standby mode. Vdd1, Vdd2 and Vdd3 correspond to the voltage levels of the first circuit block 1001, the second circuit block 1002 and I/O circuit part 1003, respectively. When entering the standby mode from the regular active mode, power supply to the second circuit block 1002 is stopped and only the first circuit block 1001 and I/O circuit part 1003 operate. The first circuit block 1001 contains a circuit which controls switching to the active mode and a memory for storing data necessary to return to the active mode.
In the above semiconductor circuit apparatus, the thicknesses of gate insulating films of respective circuit blocks may be set to different values. Specifically, it follows: I/O circuit part 1003>first circuit block 1001>second circuit block 1002. Thinner gate insulating films of the second circuit block 1002 which operates in the active mode allow high speed operation of the circuit block. Furthermore, thicker gate insulating films of the first circuit block 1001 and I/O circuit part 1003 which operate in the standby mode afford a reduction in leak current and reduction in power consumption in the standby mode. A semiconductor circuit apparatus configured as above is disclosed in Japanese Published Unexamined Patent Application No. 2003-188351. Besides, Japanese Published Unexamined Patent Application No. 2001-156260, for example, discloses a technique varying the gate insulating film thickness from circuit block to circuit block.
The above mentioned circuit configuration can reduce the power consumption by using the standby mode. It has now been discovered that in the transition to the standby mode in the above semiconductor circuit apparatus, it is needed to fix input signals from the second circuit block 1002 to other circuit blocks, and also needed to clamp to ground or separate output signals from other circuit blocks to the second circuit block 1002 in order to stop the power supply to the second circuit block 1002. Thus, the sequence to stop power supply to the second circuit block 1002 is necessary, as well as an interface control circuit.
Also, a regular power-on sequence is needed to return from the standby mode to the active mode and resume the power supply to the second circuit block since each node level is undefined. The circuit configuration and sequence for mode switching is thus complicated, and it takes long time to go into the active mode from the standby mode. And, the leak current control by changing only the thickness of a gate oxide film can not meet the requirements of both the operation performance during the active mode and leak current reduction during the standby mode.